1. Field of the Invention
The present invention relates to a printing medium suitable for use in printing with inks. In particular, the present invention relates to a printing medium for ink-jet, which can provide images high in optical density and bright in color tone, scarcely causes beading even when using inks comprising a surfactant to improve their penetrability into printing media, and has excellent ink-absorbing capacity, a production process thereof, and an image-forming process using this medium.
2. Related Background Art
In recent years, an ink-jet recording system, in which minute droplets of an ink are flown by any one of various working principles to apply them to a printing medium such as paper, thereby making a record of images, characters and/or the like, has been quickly spread as a recording apparatus for various images in various applications including information instruments because it has features that printing can be conducted at high speed and with a low noise, color images can be formed with ease, printing patterns are very flexible, and development and fixing process are unnecessary.
Further, it begins to be applied to a field of recording of full-color images because images formed by a multi-color ink-jet system are comparable in quality with multi-color prints by a plate making system and photoprints by a color photographic system, and such printed images can be obtained at lower cost than the usual multi-color prints and photoprints when the number of copies is small.
With the improvement in printability such as speeding up and high definition of printing, and full-coloring of images, printing apparatus and printing methods have been improved, and printing media have also been required to have higher properties. This requirement has offered problems to be solved.
In order to solve such problems, a wide variety of printing media has heretofore been proposed. For example, Japanese Patent Application Laid-Open No. 52-53012 discloses paper for ink-jet, in which a base paper web having a low sizing degree is impregnated with a surface coating. Japanese Patent Application Laid-Open No. 53-49113 discloses paper for ink-jet, in which a sheet containing urea-formalin resin powder therein is impregnated with a water-soluble polymer. Japanese Patent Application Laid-Open No. 55-5830 discloses paper for ink-jet recording, in which a coating layer having good ink absorbency is provided on a surface of a base material. Japanese Patent Application Laid-Open No. 55-51583 discloses that non-crystalline silica is used as a pigment in a coating layer. Japanese Patent Application Laid-Open No. 55-144172 discloses an image-receiving sheet having a coating layer containing a pigment which adsorbs a coloring component in a water-based ink. Japanese Patent Application Laid-Open No. 55-146786 discloses that a coating layer formed of a water-soluble polymer is used.
In U.S. Pat. Nos. 4,879,166 and 5,104,730, and Japanese Patent Application Laid-Open Nos. 1-97678, 2-276670, 5-24335 and 6-297831, there have been proposed recording sheets each having an ink-receiving layer in which an alumina hydrate of a pseudoboehmite structure is used.
However, the ideas described in the above documents only relate to the improvement of properties such as ink absorbency, resolution, optical density, coloring ability, color reproducibility and transparency, and these documents do not describe anything about problems of beading which tends to markedly occur at printed areas on printing media when using inks comprising a surfactant, and means for solving such problems.
The term xe2x80x9cbeadingxe2x80x9d as used herein refers to a phenomenon caused by the fact that droplets of inks applied to a printing medium aggregate into larger droplets in the course of absorption and/or the like. It is said that beading readily occurs in particular on media low in ink absorbency or slow in fixing speed of a dye in an ink. This beading phenomenon is visually recognized as color irregularity about the size of a bead.
In a printing medium provided with an ink-receiving layer, beading is observed on the surface of the ink-receiving layer or in the interior of the ink-receiving layer.
There are the following problems in the conventional measures for the beading.
1. Japanese Patent Application Laid-Open Nos. 55-29546 and 6-24123 each disclose recording inks, in which a surfactant is added into the inks in a proportion ranging from several percent to ten-odd percent so as to improve the penetrability of the ink. These inks have an advantage that they can be used in printing on plain paper having a comparably high sizing degree. However, when printing is conducted with these inks on a porous ink-receiving layer comprising, as an principal component, a alumina or silica material, there arises a problem that the absorption of the inks becomes poor, or beading occurs. In particular, in an ink in which the concentration of the surfactant is increased near to a critical micelle concentration so as to enhance its penetrability, the ink components applied tend to aggregate on the ink-receiving layer to cause beading.
2. Japanese Patent Application Laid-Open Nos. 58-110287, 60-137685, 60-245588 and 02-276670 each disclose a printing medium in which the porous structure, such as pore radius distribution and pore volume, of an ink-receiving layer are adjusted to increase its ink-absorbing rate and ink absorption quantity.
Japanese Patent Application Laid-Open Nos. 05-024335 and 06-297831 each disclose a printing medium having an ink-receiving layer composed of pseudoboehmite and a binder, in which the thickness of the ink-receiving layer, a ratio of the pigment to the binder and a coating weight of the receiving layer are adjusted to increase its ink-absorbing rate and ink absorption quantity.
These are based on an idea that the ink-absorbing rate is increased, thereby preventing beading. However, the occurrence of beading also depends upon the fixing quantity and speed of a dye in an ink, so that the occurrence of beading cannot be prevented only by the increase of the ink-absorbing rate. Further, these documents do not describe anything about the measures for beading occurring upon the use of inks containing a surfactant.
3. Japanese Patent Application Laid-Open Nos. 57-173194, 60-046290, 63-151477, 04-115983 and 04-122672 each disclose a printing medium using a resin material having high solvent absorbency, while Japanese Patent Application Laid-Open Nos. 60-171190, 61-132376 and 03-043291 each disclose a printing medium to which a surfactant and the like are added.
These are based on an idea that a material high in ink absorbency or ink-diffusing ability is used to improve the absorption of ink. However, the beading phenomenon is also caused by aggregation of a dye in an ink, so that the occurrence of beading cannot be prevented only by the improvement of the ink absorbency. Further, these documents do not describe anything about the measures for beading occurring upon the use of inks containing a surfactant.
4. Japanese Patent Application Laid-Open No. 55-144172 discloses a printing medium provided with a receiving layer containing a pigment which adsorbs a dye in an ink, Japanese Patent Application Laid-Open No. 60-232990 a printing medium provided with an ink-receiving layer containing cationic aluminum oxide, Japanese Patent Application Laid-Open No. 62-264988 a printing medium containing a material which precipitates a dye in an ink, and Japanese Patent Application Laid-Open No. 01-097678 a printing medium using a substance having an adsorbing capacity of from 20 to 100 mg/g in combination with an ink absorbent.
These are based on an idea that the material high in adsorbing capacity is used to increase the adsorption quantity and adsorption rate of a dye in an ink. The water fastness of images printed is improved. However, since the quantity of the dye to be adsorbed on the ink-receiving layer also depends upon the specific surface area and coating weight of a material from which the receiving layer is formed, and low ink absorption also forms the main cause of beading, the occurrence of beading cannot be prevented only by the use of a material the dye-adsorbing capacity of which has been regulated. Further, these documents do not describe anything about the measures for beading occurring upon the use of inks containing a surfactant.
5. Japanese Patent Application Laid-Open No. 55-005830 discloses a printing medium in which the absorbency of an ink-receiving layer is within a range of from 1.5 to 1.8 mm/min, Japanese Patent Application Laid-Open No. 60-224580 a printing medium provided with an ink-receiving layer containing synthetic silica the surface of which has been treated with a silane coupling agent, Japanese Patent Application Laid-Open Nos. 60-260376 and 63-252779 each a printing medium to which a fluorine-containing surfactant or water-proofing and oil-proofing agent is added, and Japanese Patent Application Laid-Open Nos. 61-237682, 62-204990, 01-133779, 01-222985 and 02-117880 each a printing medium in which a hydrophobic substance is added in the interior of an ink-receiving layer composed of a hydrophilic resin, or on the surface thereof, or a hydrophobic part is provided on the surface of an ink-receiving layer. Besides, Japanese Patent Application Laid-Open Nos. 03-045378 and 03-130187 each disclose a printing medium provided with an ink-receiving layer the contact angle with an ink or the like of which is adjusted. These are based on an idea that the wettability of the surface of the ink-receiving layer is adjusted, whereby a dot diameter of an ink droplet applied is reduced to prevent ink droplets adjacent to each other from aggregating before the ink is absorbed.
However, the method of adjusting the wettability of the surface involves a problem that since its ink-absorbing rate becomes low, the resulting printing medium tends to cause beading when the quantity of an ink ejected on the printing medium increases. Further, these documents do not describe anything about the measures for beading occurring upon the use of inks containing a surfactant.
It is an object of the present invention to provide a printing medium which can suppress the occurrence of beading and feathering or bleeding even when using inks comprising a surfactant, has good ink absorbency, permits a choice of inks in a wide range, can provide images high in optical density, has good transparency when a transparent base material is used in that no difference arises in optical density and coloring of the resulting image between the observation from the side of an ink-receiving layer and the observation from the side of a base material or between the observation by reflection and the observation by transmission, and scarcely causes cracking or curling, an image-forming process using this printing medium, and a production process of the printing medium.
The above object can be achieved by the present invention described below.
According to the present invention, there is thus provided a printing medium provided on a base material with a porous ink-receiving layer which comprises, as principal components, an alumina hydrate having a boehmite structure and a binder, wherein when measuring with an ink containing 0.1% by weight of a surfactant, the time required to absorb 30 ng of the ink is 400 milliseconds or shorter, the dye-adsorbing capacity falls within a range of from 900 to 2,000 mg/m2, and the index of dye-adsorbing rate falls within a range of from 0.0 to 5.0.
According to the present invention, there is also provided an image-forming process comprising the step of ejecting droplets of inks from ejection orifices of a printing head in response to printing signals to apply the ink droplets to the printing medium described above.
According to the present invention, there is further provided a process for producing the printing medium described above, comprising the steps of applying a dispersion comprising an alumina hydrate having a boehmite structure and a binder to a base material and drying it, thereby forming an ink-receiving layer, and heating the ink-receiving layer.
According to the present invention, there is still further provided a process for producing the printing medium described above, comprising the steps of preparing a mixed dispersion by adding at least one selected from the group consisting of metal alkoxides and materials capable of crosslinking a hydroxyl group to a dispersion comprising an alumina hydrate having a boehmite structure and a binder, applying the mixed dispersion to a base material and drying it, thereby forming an ink-receiving layer, and heating the ink-receiving layer.
According to the present invention, there is yet still further provided a process for producing the printing medium described above, comprising the steps of applying a dispersion comprising an alumina hydrate having a boehmite structure and a binder to a base material and drying it, thereby forming an ink-receiving layer, applying a liquid containing at least one selected from the group consisting of metal alkoxides and materials capable of crosslinking a hydroxyl group to the ink-receiving layer, and heating the ink-receiving layer.